PIXE-PIGE analysis of early medieval window glass from the abbey of Stavelot

From the 1 st century, glass found in northern Europe was made from a mix of sand and natron that had to be imported from eastern Mediterranean [1]. After the fall of the Roman Empire, glassmakers could either recycle existing glass or continue to import material. Then, around the end of the 8 th century, the first testimonies of potash glass, made with sand and trees ashes, are attested [1]. This type of glass would then prevail but the reasons and mechanisms of its appearance remain beyond understanding. They could be linked to the development of architecture and the growing needs of window glass. Founded in the middle of the VII th century, the abbey of Stavelot was a first time ruined by Vikings in 881. In the destruction levels, hundreds fragments of window glass were found [2]. 34 fragments were analysed in PIXE-PIGE at the cyclotron of the Institute of Nuclear and Atomic Physics and of Spectrometry of the University of Liège. The results show coexistence of both natron and potash glass on the site, even in the same archaeological contexts. For the coloration, the recipes to obtain turquoise or amber glass were comparable to those known on other early medieval sites [3], but to make green potash glass the artisans have used to two types of recipes. This shows the need to carry on researches and analysis on early medieval window glass in order to understand its production techniques that are also at the origin of famous gothic stained glass